The objective of this research project is to identify and characterize cell surface glycoproteins of mouse lymphocytes with a long-term goal of understanding lymphocyte differentiation and function. Work has continued on preparing monoclonal antibodies against cell surface molecules that may be of functional significance. One murine monoclonal antibody, designated 140/25, has been obtained that reacts with a clonotypic determinant of the putative T-cell receptor expressed on a human T leukemic cell line, HPB-MLT. The antibody precipitates a cell surface glycoprotein with an Mr of approximately 90,000 from lysates of 125I-labeled cells that consists of two disulphide-bonded subunits of Mr = 40,000 and 49,000. The monoclonal antibody has been used to purify the putative T-cell receptor from HPB-MLT cells, and attempts to prepare additional antibodies against framework determinants of the human T-cell receptor are in progress. Another murine monoclonal antibody has been obtained against the human IL-2 receptor by immunization of mice with the human T-cell line, HUT 102; and the expression of the IL-2 receptor on human leukemic cell lines has been studied. Treatment of some human T-leukemic cell lines with phorbol ester induces the expression of IL-2 receptors that differ in apparent molecular weight from those expressed upon HUT 102 cells. The structural basis for this difference is under investigation. (LB)